1. Field of the Invention
This invention relates to centrifugal pumps of the pitot tube type, and specifically relates to such pumps having improved construction to axially stabilize the pick-up tube and discharge assemblies to minimize damage and wear.
2. Statement of the Art
Centrifugal pumps are commonly known in the art and are frequently used in a wide variety of industries to process fluids. Centrifugal pumps of the pitot tube type conventionally include a housing, a rotary casing attached to a drive unit, a stationary pitot tube, an inlet and a discharge or outlet. Fluid entering the pump through the inlet is at a comparatively low pressure (e.g., 100 psi) and is subjected to centrifugal forces as the fluid encounters the rotary casing. The increased pressure (e.g., 500 psi) of the fluid at the periphery of the rotary casing, coupled with the ram effect imposed on the fluid by the positioning of the pitot tube relative to the rotary casing, causes the fluid to enter into the inlet of the pitot tube. The pressurized fluid travels through the pitot tube and into the discharge assembly where it exits the pump. At that point, the fluid may be, for example, at a pressure of 750 psi or higher. The fundamental elements and operation of a pitot tube pump are well known to those skilled in the art.
Pitot tube pumps differ in configuration and construction, but all are subject to wear and degradation as a result of the increased pressures imposed on the fluids being processed through the pump. For example, the increased pressure resulting from centrifugal forces causes thrust loads or axial loads to exist in the housing, in the rotary casing and in the pitot tube and discharge assembly. U.S. Pat. No. 3,822,102 to Erickson et al., U.S. Pat. No. 4,183,713 to Erickson, et al., and U.S. Pat. No. 4,279,571 to Erickson each disclose pitot tube pump configurations which recognize and address thrust loads experienced in the housing, typically near the drive shaft end of the rotary casing. In particular, those patents disclose pumps that are structured with improved thrust bearings or thrust balance means to alleviate the damaging loads.
Axial loads are experienced along the longitudinal axis of the pitot tube and discharge tube thereof due to the high discharge pressures generated by the pump. In addition, radial, tangential, and axial loads are experienced by the pickup tube head and wing as a result of hydraulic forces within the rotating casing itself. The support mechanism of a pitot tube assembly must resist all of these forces. Among the types of damage which may be experienced in a conventional pitot tube pump are a vibration or wobbling of the pitot tube which causes structural failure in the pitot tube, fretting and galling which occurs on the pitot tube and discharge assemblies, fatigue failure or loosening and loss of the mounting bolts and stress failures in the material of the inlet manifold. In some pump configurations, the degrading effects of axial loads are compounded by the cantilevered positioning of the pitot tube within the inlet/outlet manifold. In addition, conventional configurations of pitot tube pumps use very expensive bolts to attach the pitot tube to the manifold thereby significantly increasing the cost of the pump. The time required to fix or maintain the pump can be a significant limiting factor to efficient operation as well.
Thus, it would be advantageous in the art to provide a centrifugal pump of the pitot tube type which is structured to reduce axial forces in the discharge assembly to thereby stabilize the pitot tube and discharge assembly and to provide a pump construction having improved mechanical stiffness and one which is more easily repaired and maintained.